The present invention generally relates to processing a semiconductor substrate. In particular, the present invention relates to maximizing semiconductor device yield by utilizing a wafer-integrated monitoring system to adjust a metal etch process and/or a CMP process.
Achieving the objectives of miniaturization and higher packing densities continue to drive the semiconductor manufacturing industry toward improving semiconductor processing in every aspect of the fabrication process. One such aspect of the semiconductor fabrication process is subtractive metallization or metal etch processes. Metallization typically refers to forming metal layers, whereas subtractive metallization typically refers to removing metal to form conductive lines, interconnects, contact holes and plugs. In addition, subtractive metallization can also involve etching or chemical mechanical polishing (CMP) of the metal material in order to obtain desired thicknesses and structures. The CMP process removes or planarizes selected portions of the metal material. In both the metal etch and polishing processes, conventional endpoint detection techniques are often used to determine when the etch or polish is completed in order to prevent malformation of the desired structure or feature on the wafer. For example, prior art FIGS. 1-3 and 4-6 demonstrate malformed features on the wafers resulting from a metal etch process and a CMP process, respectively, wherein conventional endpoint detection techniques are employed.
FIGS. 1-3 illustrate a wafer 10 undergoing a metal etch process whereby the metal layer 12 which is formed over a substrate 14 is exposed to etch components 16. The resulting wafer structure 20 reveals incompletely etched conductive lines 22. In other words, metal material 24 continues to undesirably exist between the conductive lines 22. This excess metal material 24 may disform the wafer structure and impair proper semiconductor function.
Likewise, incomplete polishing of a metal material can also result in ineffective semiconductor function. FIGS. 4-6 illustrate a metal layer 32 formed over a series of trenches 34 between a dielectric material 31 on a substrate 30. The metal layer 32 undergoes a CMP process 36 to remove excess metal material, leaving metal only in the trenches (FIG. 5). However, incomplete polishing 38 resulting from faulty endpoint detection methods such as that shown in FIG. 6 can render the device inoperable or impaired. Thus, it is crucial to the operability of semiconductor devices to minimize insufficient or excessive processing of the wafer.
Conventional endpoint detection techniques are problematic for several reasons. For instance, they often are based on past wafer characteristics. Such methods cannot account for wafer to wafer structural and layer variations which commonly exist. As a result, conductive lines, interconnects, contacts holes and/or plugs are malformed and defective, causing device failure and decreased product yield as well as varying wafer-to-wafer quality. Although some damaged wafers may be repaired, such repairs delay manufacturing, increase production costs and decrease product reliability. In addition, conventional endpoint detection methods do not provide real time information relating to the current etch or polishing process.
In light of these problems, there is an unmet need for a monitoring system which may provide improved feature formation and endpoint detection.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides a novel monitoring system and method for endpoint detection with respect to metal etch and CMP processes. More specifically, the present invention provides a closed loop, real-time feedback system for detecting the endpoint of a given subtractive metallization process as the process progresses. For example, a metal etch process is substantially completed when no electrical activity is detected on the wafer or at the desired locations of the wafer. This is accomplished in part by employing electrical sensors embedded on and/or embedded in the wafer. The electrical sensors operate by detecting electrical activity within the wafer. In particular, the electrical sensors detect electrical activity such as current flow and resistance arising from the surrounding metal layer material formed on the wafer. As selected portions of the metal are etched, the sensors may continue to perform continuity tests and/or detect for electrical activity to determine the extent the etch process is completed. Likewise, the absence of electrical activity may be acknowledged in a similar manner. No electrical activity may be an indication that the metal material has been removed as desired. Before, during and following the subtractive metallization process, the electrical activity on the wafer may be monitored.
One aspect of the present invention relates to a system for monitoring a subtractive metallization process in real-time in order to effectuate an immediate response and modification in an on-going subtractive metallization process. The system contains a wafer comprising at least one metal layer formed on a semiconductor substrate, at least one electrical sensor in contact with the wafer and operable to detect and transmit electrical activity associated with the wafer, and an electrical measurement station operable to process electrical activity detected and received from the electrical sensor for monitoring a subtractive metallization process in real-time.
Another aspect of the present invention relates to a method for monitoring a subtractive metallization process in real-time includes providing a wafer comprising a layer of metal material formed over a semiconductor substrate, the wafer being in contact with at least one electrical sensor embedded at least one of on the wafer and in the wafer, subjecting the metal layer to a process selected from the group consisting of an etch process and a chemical mechanical polishing process, and determining the presence of electrical activity on the wafer to monitor the progression of the process in order to determine an endpoint of the process.
Yet another aspect of the present invention relates to a wafer which may be employed in the system and method described above. The wafer contains a semiconductor substrate, at least one metal layer formed over the semiconductor substrate, and at least one electrical sensor embedded at least one of on the wafer and in the wafer to facilitate real-time monitoring of the metal layer as it progresses through a subtractive metallization process.